I filtered my photos by the aspect ration of portrait while using develop mode on two screens. During a photo edit with the crop tool, 'X' works to rotate the rotate the crop tool. In this case while use the corp tool before you are 'done' the image disappears. My guess the metadata changes to landscape before you are finished with the tool. I was able to work around the issue by disabling the filter and going to 'Loupe' mode.